Preparation of adlay (Coix lacryma-jobi L.) starch nanoparticles by food-grade Fenton-assisted ultrasonication: structure–property relationships and potential as Pickering nanoemulsions stabilizers

Adlay ( Coix lacryma-jobi L.) starch nanoparticles (SNPs) were fabricated using a sonication/ultrasound-assisted metal-free Fenton employing gallic acid (GA) and H₂O₂. Effects of GA concentration and sonication duration on particle characteristics, colloidal stability, and structural properties were systematically investigated. Treatment employing 35 mM GA and 30 min sonication (LCF-30) produced a number-weighted primary particle size of 70.5 nm, high polydispersity (PDI 0.745 ± 0.035), and an intensity weighted Z average of 1107 ± 85 nm. The elevated PDI reflects a broad, heterogeneous aggregate-containing system rather than a monodisperse suspension, capturing a balance between cavitation-induced mechanical fragmentation and radical depolymerization. Prolonged sonication increased surface charge heterogeneity, including (−30 mV), attributed to localized oxidation heterogeneity and trace matrix impurities. X-ray diffraction confirmed the A-type crystalline polymorph across all treatments (crystallinity index 27.6%–33.3%), while FTIR spectroscopy revealed carbonyl group formation and a reduction in the 989 cm −1 C O C band, confirming selective glycosidic bond scission.